Injection molding of cone-shaped covers for small consumer products (e.g., covers for closed-face spincast fishing reels) are known. Such covers are typically made of plastic or epoxy with injection molding being the process of choice in the manufacture of such articles.
It is known that in the making of such articles through injection molding, the best yield (i.e., the fewest number of defects) occurs when the plastic is injected at a single, common point and mold filling occurs along a single front of plastic progression. Where the single front of injected plastic is forced to flow around an obstacle (e.g., where an aperture is to be formed in the cover), the single front of plastic is divided into two fronts as plastic flows around each side of the obstacle. As the two fronts flow around the obstacle, they ultimately meet and merge at the far side. Where the two fronts merge, the cooler plastic along the surface of the fronts usually forms a visible seam at the point of contact. The visible seam is referred to as a knit mark or flow mark. The seam in many cases represents a cosmetic defect that usually results in the part being rejected.
Another source of defects occurs where plastic flow stops along a portion of the front in one part of the mold while progression continues in other parts of the mold. Where the flow has stopped, the plastic rapidly cools and solidifies. Where the flow continues, the plastic along the front remains relatively hot and fluid. Where transition points exist between the flowing hot plastic and the stationary, cooler plastic, cracks occur due to differential cooling.
In making covers for closed-faced spincast fishing reels, the injection point (gate) is typically chosen as the area of the tip of the cone-shaped cover where an aperture must later be created through which the fishing line passes (the line aperture). Injection of the plastic typically occurs around a periphery of what will later become the line aperture. After the mold has been filled and the plastic cools, the line aperture is blocked with a puddle of plastic, which must later be removed. The injection of plastic into a mold through such a gate is commonly referred to as a puddle gate. Following injection and cooling, the line aperture is drilled or punched out to create the finished line aperture.
Alternatively, the thickness of the mold gate is restricted around the periphery of the line aperture in what is referred to as a fan aperture. Narrowing the thickness of the cover wall around the periphery of the line aperture reduces the difficulty of later drilling or punching out the finished hole.
While the use of puddle or fan gates around the periphery of a fishing line aperture has been effective in creating covers for closed-face spincast fishing reels, the process is costly and subjects the injected cover to the possibility of other process induced defects in later drilling or punching stages.
Accordingly it is an object of this invention to provide a process and apparatus of injection molding covers with apertures that is less susceptible to the defect rates of previous processes.
It is a further object of the invention to provide a process that has the additional benefit of not requiring the additional steps of drilling or punching for creation of the aperture.